Electric initiator



Jan. 6, 1953 D. 'r. ZEBREE ELECTRIC INITIATOR Filed Jan. 9, 194a flai/'0" T Zebree INVENTOR.

AGENT struction and performance. a continuation-in-part of co-pendingapplication Serial No. 574,349, filed January 24, 1945, now issued as U.S. Patent 2,473,405.

-ject to failure. failure certain limitations have been imposed upon thedesign and use of the initiators. example, if substantial gas pressureis developed Patented Jan. 6, 1953 ELECTRIC INITIATOR David T. Zcbree,Kingston, N. Y., assignor to Her- 2 cules Powder Company, Wilmington,DeL, a

corporation of Delaware Application January 9, 1948, Serial No. 1,354

9 Claims.

This invention relates to electric blasting initiators and moreparticularly to delay electric initiators containing an improvedignition composition and to initiators having improved con- Thisapplication is In delay electric initiators known to the art, it is mostcommon to use a bronze shell with an upper inside diameter of about 0.30inch stepped down to about 0.25 inch, a base charge of'pentaerythritoltetranitrate or tetryl, or the like, a

priming charge of diazodinitrophenol, mercury fulminate, or the like,plus an oxygen carrier, a fuse, an air space, and an ignition assemblywith a cavity-type plug containing a flash mixture, usuallydiazodinitrophenol in conjunction with potassium chlorate, charcoal, andnitrostarch, or a matchhead-type ignition assembly consisting of a beadof copper acetylide on a bridge wire set in sulfur and enclosed in apaper cylinder or a bead comprising a lead salt of dinitro-orthocresol,smokeless powder, and potassium chlorate on the bridge wire. A layer ofwaterproofing and sulfur above the plug completes the assembly of theusual types. However,

delay initiators known to the art have been sub- To preclude thepossibility of For within an initiator upon firing, the shell is apt torupture or the ignition assembly is apt to be blown'from the shell.f'hus, the shell must be vented, or a suitable air space or absorbentmaterial must be provided, or the shell and the ignition assembly mustbe of sufficient structural strength to withstand the pressure.Moreover, high gas pressure within an initiator is apt to alter itsfiring characteristics. For obvious reasons, the ventless-type initiatorwithout an air space is preferred. This combination eliminates thepossibility of moisture reaching the charges of the initiator andaffords economy in manufacture, since the elimination of the air spacepermits shortening of the length of the initiator. In addition, theelimination of the air space improves an initiator for high voltagefiring. In high voltage firing arcing accompanies many shots. Thisarcing occurs in the vicinity of the ignition assembly and punctures theshell of the initiator. When an air space is provided between theignition assembly and the fuse, a rapid escape I of the ignition heatthrough the puncture above the fuse contacts the fuse regardless of thepuncture and positive firing and normal ignition time are obtained.

The objectives sought in the manufacture of initiators are ease ofassembly, economy of material, and improved performance. The objectivesare not attainable by increasing the structural strength of an initiatorto withstand high internal gas pressure. Accordingly, a reduction of theinternal gas pressure in an initiator and an improved initiatorconstruction as a result thereof, is a definite contribution to the art.

Thus, it is the principal object of the present invention to provide animproved ignition composition which generates a minimum amount of gas incontrast to prior art ignition compositions.

It is another object of this invention to provide an initiator ofimproved construction and performance for normal or high voltage firing.

Other objects of the invention will appear hereinafter, the novelfeatures and combinations being set forth in the appended claims.

Now in accordance with this invention, the improved ignition compositioncomprises primary explosive, oxidizing material, heat-producingmaterial, and binding agent, wherein the particle size of the oxidizingmaterial is not greater than about 74 microns and the oxidizing materialis present in amount not greater than about 15% by weight of theignition composition.

The improvement in delay electric initiators in accordance with thisinvention essentially comprises a fuse charge having superimposed thereon the ignition composition of this invention.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawing.In the drawing, there is illustrated a part sectional, part elevationalview of a delay electric initiator in accordance with this invention.

With reference to the drawing, a ventless metal shell ID has a basecharge ll pressed in the bottom thereof. A priming charge I2 is placedover the base charge I l and a fuse charge [3 is inserted into the shelll0 and pressed upon the priming charge. The fuse charge I3 consists of alead tube having a fuse powder [5 therein. An ignition assembly l6 waspressed upon the fuse charge 13. The ignition assembly It comprises aplug member I! having a cavity l8, a pair of leg wires 19 connected attheir terminal ends 20 by a bridge wire 2 I, and an ignition composition22 placed in the cavity and subject to ignition by the bridge wire whenelectrical current is imparted to the leg wires.

The practical application of this invention is illustrated in thefollowing examples:

Earample 1 A bronze shell having an indented bottom and an insidediameter in the order of 0.25 inch was loaded with a base charge of 0.40gram of pentaerythritoltetranitrate and pressed. A priming charge of0.30 gram of a mixture of 75% diazodinitrophenol and 25% potassiumchlorate was placed over the base charge. A fuse containing 84% bariumperoxide and 16% powdered selenium was placed in a lead tube which wasthen swaged so that the mixture had a density of about 4.4 g./cc. Thistube was cut into units inch long and each unit comprised a fuse charge.The fuse charge was placed upon the priming charge and pressed.

An ignition composition of 16% diazodinitrophenol, 62% bariumperoxide-selenium mixture, 10% potassium chlorate having a particle sizenot greater than '74 microns, 10% charcoal, and 2% nitrostarch was used.The barium peroxideselenium mixture used was 70% barium peroxide andselenium. The ingredients of the ignition composition were thoroughlymixed and then made into a paste by wetting with butyl acetate. Thispaste was then buttered into a cavity-type plug provided with leg wiresand a bridge wire. The cavity was A; inch long, T175 inch wide, and inchdeep. After the paste was dried, the ignition assembly was placed uponthe fuse charge. A waterproofing compound and sulfur seal applied in theconventional manner completed the initiator.

Example 2 Delay electric initiators were prepared exactly as describedin Example 1, with the exception that the ignition composition contained16% diazodinitrophenol, 57% barium peroxide-selenium mixture, 15%potassium chlorate having a particle size not greater than 74 microns,10% charcoal, and 2% nitrostarch.

Emample 3 Example 4 Delay electric initiators were prepared exactly asdescribed in Example 1, with the exception that the ignition assemblycomprised a plug of hard dielectric material which was forced into theshell and firmly pressed upon the fuse charge.

In this example, the shell was shortened leaving a slight projecting rimafter the ignition assembly was fully inserted. This rim was rolled overthe top of the plug to complete the initiator. This constructioneliminated the waterproofing compound and sulfur seal, therebyconsiderably 4 shortening the shell, and constitutes the preferredembodiment of the invention as shown in the drawing.

With reference to the above examples, it was found that the ignitioncomposition of this invention superimposed upon the fuse charge gaveinitiators that surpassed prior art initiators in general performance.This was particularly noted in high voltage firing where a series of 25single shots were made at 440 volts A. C. without a failure. Prior artdelay initiators are recognized as subject to failures when fired underthese conditions. In a series of prior art delay initiators tested on acomparable basis, 45% of the initiators failed to fire. Since theignition composition of this invention develops an extremely lowinternal pressure within the cap, conventionally assembled initiatorsemploying this composition have an increased factor to insure positivefiring and conventionally assembled initiators may be lightened inconstruction without sacrificing performance. Moreover, since thevarious charges may be pressed one upon the other, case of assembly andpermanence of position for the relative charges are obtained. Inaddition, it will be noted that the shells were of substantially uniformdiameter throughout their length, thereby eliminating the stepped downconstruction employed with. prior art devices.

In accordance with this invention, the base charge may bepentaerythritoltetranitrate, tetryl, nitrostarch, nitromannite, and thelike. Pentaerythritoltetranitrate is preferred. The priming charge maybe diazodinitrophenol, mercury fulminate, lead styphnate, silver azide,lead azide, and the like. Diazodinitrophenol is preferred. The fusepowder may be a mixture of a metallic oxide and a material such asselenium or tellurium. A mixture of about 84% barium peroxide and 16%selenium, by weight, compressed to a density in the order of 4 g./cc. ina metal tube is preferred. The fuse may be cut to various lengths togive fuse charges of predetermined intervals for delay firing.

The ignition composition in accordance with this invention essentiallycontains not more than about 15% by weight of an oxidizing materialhaving a particle size not greater than about 74 microns. It is wellknown in the art that ignition compositions are capable of considerablemodification. Regardless of the latitude afforded in formulation, itisstillcustomary and necessary in the manufacture of prior art devicesto add a relatively high percentage of an oxidizer to the ignitionmixture to achieve satisfactory ignition. On account of using so much ofthis ingredient, an air chamber between the fuse and ignition assemblymust be provided to accommodate the gases produced from the mixture uponignition or other means such as heretofore described must be utilized.However, in accordance with this invention, it has been found thatconsiderably less oxidizer is equally effective if this ingredient isvery fine (maximum diameter about 74 microns) and intimatelyincorporated in the ignition composition. As a result of using lessoxidizer, the ignition composition is appreciably less violent, andhence may be used in ventless delay initiators having no air chamber.The addition of barium peroxide-selenium mixture to the primaryexplosive and oxidizer appears to further reduce the violence of theignition mixture. Barium peroxide-selenium also appears to increasetheheat content of the ignited composition. It further appears that whena carbonaceous material is added to the composition, the burning rate isretarded. Consequently, this makes it possible to obtain good seriesfiring. The binding agent serves to hold the ignition composition inplace when used in conjunction with a cavity-type plug.

Very satisfactory results may be obtained in accordance with thisinvention when using from about to about 20% primary explosive, fromabout 50 to about 70% heat-producing material, from about 5 to aboutoxidizing material, from about 5 to about 15% carbonaceous material, andfrom about 1 to about 5% binding agent.

The primary explosive may be finely divided explosives such asdiazodinitrophenol, mercury fulminate, lead styphnate, and silver azide.Diazodinitrophenol of flash grade is preferred. This grade containsparticles which range from about 50 to about 150 microns in diameter.

The heat-producing material should be a material for which the valuesfor heat content and for free energy of formation of the oxides arehigh. Thus, mixtures of an oxidizing agent such as barium peroxide,potassium chlorate, potassium permanganate, or the like with an elementsuch as selenium, tellurium, sulfur, or the like may be used. However,flash-producing metals such as aluminum, chromium, tin, copper,magnesium, or the like, such as disclosed in copending applicationSerial No. 574,349, may be used as a substitute for the mixtures,although the metals are less satisfactory. While these metals doincrease the heat content, they do not assist in reducing the violenceof the ignited composition as do the above mixtures. The ingredients forthe heat-producing material should be finely divided to insure intimatemixture in the ignition composition. A mixture of commercial gradebarium peroxide with selenium powder in a ratio of 70-30%, by weight, ispreferred in which the particle size of the peroxide is not more than0.10% on a U. S. Standards No. 200 sieve and on a No. 325 sieve, and forthe selenium not more than 1% on a No. 200 sieve and 10% on a No. 325sieve.

Although a number of oxidizing compounds known to the art may beemployed as the oxidizing material, such as dichromates (potassium andsodium dichromates), nitrates (sodium, potassium, and barium nitrates),oxides, such as copper oxide, perchlorates, such as sodium and potassiumperchlorate, it is preferred to employ potassium chlorate, potassiumnitrate, or potassium permanganate. The preferred compounds will befound to be superior to the other compound particularly in consistentperformance at high temperatures. Potassium chlorate having a particlesize diameter from about 10 to about '74 microns has given excellentresults and is preferred.

The carbonaceous material may be charcoal, lampblack, or the like infinely divided form. Willow charcoal dust has been found quitesatisfactory and is preferred. The carbonaceous material may be omittedfrom the ignition composition, but as pointed out heretofore it appearsto improve the characteristics of initiators fired in series.

As the binding agent, nitrostarch is preferred. However, other binderswell known to the art, such as nitrocellulose, may be used.

In preparing the ignition composition heretofore described theingredients are thoroughly mixed and then made into a paste by wettingwith a volatile organic solvent such as butyl acetate to obtain thedesired consistency. The composition is then buttered into the cavity ofan ignition plug and then allowed to dry.

The shell material as employed in preparing the initiators of thisinvention may be the standard materials employed in the art, such asbronze, copper, or aluminum. The plug materials may be either softer orharder than the shell casing and include sulfur, plastic compositionssuch as rubber, and synthetic resins such as phenolformaldehyde resins,polystyrene resins, and ethyl cellulose. The plugs may be sealed in theshell using a water-proofing composition, with a sulfur seal, ifdesired, However, this is not necessary with rubber or resin plugs asexemplified by the preferred embodiment of this invention. The leadwires employed are the customary wires used in the art and may be copperor iron, plain tin or enameled, or coated with cotton servings orplastic materials. The bridge wire used to connect the ends of the leadwires may be electrically-resistant wire such as platinum or iridium, oralloy such as nichrome, copper-nickel, platinum-iridium, and the like.

In the above description, ventless initiators of the delay type havebeen described. However, the ignition composition employed is alsoadapted for use in vented delay electric blasting initiators, electricignitors, or blasting caps, or in any such device where a minimum ofinternal gas pressure is desired upon ignition.

The advantages of the present invention are multifold. Better overallperformance is obtained, particularly at high voltages. The eliminationof the air space in conventional delay initiators using waterproofingand a sulfur seal has resulted in a reduction in length in the order ofabout -i% of an inch for each delay length and makes the step down typeshell unnecessary.

For initiators made in accordance with the preferred embodimentillustrated in the drawing, the reduction in length is much greater dueto the additional elimination of the waterproofing and sulfur seal. Theignition of the fuse is more effective because of positive contactbetween the fuse and the ignition composition. Moreover, devices made inaccordance with this invention are cheaper to manufacture and areimproved both from the standpoint of performance and appearance.

What I claim and desire to protect by Letters Patent is:

1. An ignition composition for blasting caps comprising from about 10%to about 20% of finely-divided primary explosive; from about 50% toabout 70% of a heat-producing material consisting of a finely-dividedmixture of at least one nonmetallic member of the sulfur group with asubstantially stoichiometric proportion of solid inorganic oxidizingsalt; and an additional amount of not more than 15% by Weight of apulverulent inorganic oxidizing salt having a particle size not greaterthan about 74 microns.

2. An ignition composition according to claim 1 in which theheat-producing material is a substantially stoi-chiometric mixture ofselenium and barium peroxide.

3. An ignition composition according to claim 1 in which is incorporateda binding agent.

4. An ignition composition according to claim 1 in which the additionaloxidizing agent is potassium chlorate.

5. An ignition composition according to claim 7 11111 whichthenaddition-al oxidizingragent isxpotassium: permanganate.

:6..-An ignition compositioniaccording to :claim 1 in whichtheadditional oxidizing agent is-potassiumnitrate.

.7. :An ,ignition composition .for blasting .cans. comprising 'fromabout 10% to about 20% of finely-divided diazodinitrophenol; from about50% to :about 70% of a. mixture consisting of 70 parts barium peroxide.and;80 parts selenium from-about to about 15% .of;potassiumtchlo ratehavinga particle size not greaterthan about 74:.microns; from about 5%tocabout 15%charcoal; andfromabout 1% toabout.5% nitrostarch.

:8. In ardelay electricinitiator, the improvement which comprisesan-ignition composition superimposed upon a substantially ,gasless fusechargasaicl ignitioncomposition containing from about to about 20% offinely-divided.diazodinitrophenol; ,.;from about 50% to about '7 0%'ofa'mixture consisting of 70 parts barium peroxide and .30'parts selenium;from about 5% to-about ofgpotassium chlorate having aparticle size not:greater than-about 74 microns; from about 5% to about 15% charcoal; andfrom .about*1% to about 5% nitrostarch.

-9. In-a delay electric initiator the improvement which comprises anignition composition superimposed upon a substantially g-asless fusecharge,

saidignition composition containing from about 10% to about offinely-divided primary explosive; from about to about of a heatproducingmaterial consisting of a finely-divided mixture :cf sat least :onenonmetallic member of the sulfur group with a substantiallyastoichiometric proportion of ,solid inorganic oxidizing salt; andanadditional amount ofnot more than 15% .by .weight of a pulverulentinorganic oxidizing salt having a particle size not greater than about74-.microns.

DAVID T. ZEBREE.

. REFERENCES CITED The following references-are of record in thefileofthis patent:

'UNITED STATES PATENTS Number Name Date 845,678 Bayliss Feb. 24,v 19061,797,509 Lewis Mar. 24,1931 1,928,208 Large Sept. 26, 1933 2,027,825Jacobs Jan. 14, 1936 2,036,119 Chambers Mar. 31, .1936 2,118,501 FilbertMay 24,.1938 2,123,691 Burrows July 12, 1938 2,160,469 Brunet a1 May30,1939 2,175,249 Burrows Oct. 10, 1939 2,186,427 Nash Jan. 9, 19402,363,863 Hanley Nov. 28, 1944 2,400,103 Cobb May 14, 1946 2,429,490Scherrer Oct.21, 1947 2,440,579 Frazer Apr. 27, 1948 2,467,334 Haleet-al. Apr. 12, .1949 2,473,405 Zebree .June 14, 1949 2,478,415 MillerAug. .9, 1949

1. AN IGNITION COMPOSITION FOR BLASTING CAPS COMPRISING FROM ABOUT 10%TO ABOUT 20% OF FINELY-DIVIDED PRIMARY EXPLOSIVE; FROM ABOUT 50% TOABOUT 70% OF A HEAT-PRODUCTING MATERIAL CONSISTING OF A FINELY-DIVIDEDMIXTURE OF AT LEAST ONE NONMETALLIC MEMBER OF THE SULFUR GROUP WITH ASUBSTANTIALLY STOICHIOMETRIC PROPORTION OF